Camshaft phasers for controllably varying the actuation timing of engine compression valves are well known. At present, most prior art camshaft phasers in production by or for engine manufacturers are vane-type phasers having interlocked rotors and stators. The phase relationship between the rotor and the stator may be varied by varying the relative oil volume on one side or the other of interlocked vanes via a four-way oil control valve.
Vane phasers are compact and relatively inexpensive. However, they have difficulty operating rapidly or with precision at times of low oil pressure because phasers typically are powered by parasitic use of pressurized engine lubricating oil. When the engine is idling, or is very hot, or at engine start-up, or combinations of these conditions, engine oil pressure can be very low or substantially non-existent, resulting in poor phasing control and excessive engine emissions.
What is needed in the art is a camshaft phaser system wherein phasing is achieved electromechanically without reliance on engine oil pressures.
It is a principal object of the present invention to provide camshaft phasing without resort or regard to engine oil pressures to improve engine emissions control.